The present invention relates to an apparatus for manufacturing a core for a rotational electric machine, such as a stator core or a rotor core for a motor, and, more particularly, a rotary lamination apparatus that laminates core pieces punched from thin plates, while rotatively offsetting the core pieces.
A core WA shown in FIGS. 6 and 7 is formed by layering core pieces Wa. The core WA is maintained in a layered state through engagement between a plurality of projections Pa of each of the core pieces Wa and adjacent recesses of the core piece Wa.
An apparatus for manufacturing this type of core is disclosed in, for example, Japanese Laid-Open Patent Publication No. 2006-26735 (first conventional art) and Japanese Laid-Open Patent Publication No. 2003-19520 (second conventional art).
In the first conventional art, a punch is arranged above and faces a die in a manner movable in the axial direction. As the punch reciprocates with respect to the die, a core piece is punched out from a thin plate mounted on the die. A pressing ring is arranged below the die. An axial hole extends through the centers of the die and the pressing ring, and receives a mounting table, which is movable in the axial direction of the die. After having been punched using the punch and the die, a core piece is pressed and held by the pressing ring from the outer circumference. The core piece is then mounted on the mounting table and subsequent core pieces are sequentially layered on the core piece. A core is thus manufactured. When a punched core piece is mounted on the mounting table, an elastic member arranged on the mounting table applies force acting in the opposite direction to the direction in which the punch presses, or counter pressure, to the laminated core. This prevents parallelism defect and formation of gaps between layers.
In the second conventional art, a die is rotatable. Each time a single core piece or a predetermined number of core pieces are punched by a punch and the die, the die and a pressing ring are rotated integrally with the core piece(s) at a predetermined angle. Through such rotation of the die and the pressing ring, the core pieces are layered while being rotatively offset, with offset phases. This prevents the lamination thickness of a laminated core from becoming non-uniform due to thicknesses deviation of punched core pieces.
However, the above-described conventional configurations have the problems described below.
In the first conventional art, core pieces are stacked on the mounting table in a constant phase (orientation) without being rotated after having been punched out. This causes a non-uniform lamination thickness in a laminated core, which is brought about by thicknesses deviation of the core pieces. Accordingly, if a rotor core for a motor, for example, is manufactured, rotation accuracy such as rotation balance is decreased and thus the motor characteristics are deteriorated.
In contrast, in the second conventional art, the core pieces are layered while being rotatively offset through rotation of the die and the pressing ring. The problem caused by the first conventional art is thus prevented. However, the second conventional art does not include a mounting table that applies the counter pressure to a laminated core. As a result, unlike the first conventional art, the second conventional art cannot prevent parallelism defect of the laminated core or gap formation between layers.
Alternatively, in an apparatus having a rotatable die and a rotatable pressing ring like those from the second conventional art, a mounting table may be arranged in an axial hole formed in the die, as in the first conventional art. However, in this configuration, core pieces are mounted on the mounting table while being rotatively offset through rotation of the die and the pressing ring with the mounting table held in a stationary state without being rotated. This rotates a laminated core formed on the mounting table relative to the mounting table, causing the core and the table to rub against each other. This may form an abrasion mark on a core piece. Also, when a core is already mounted on the mounting table and an additional core piece is mounted on the uppermost core piece of the core while being rotatively offset, the upper and lower cores rotate relative to each other, causing projections Pa to form a clear linear abrasion mark on the cores. The abrasion mark may influence formation of magnetic paths, thus lowering the performance of the products.